DISEASE PREVENTION INFORMATION DIETARY GUIDELINES AND TIPS ON PROPER NUTRITION
Q: Can vegetables prevent cancer?
A: The National Cancer Institute, in its booklet Diet, Nutrition, & Cancer Prevention: A Guide to Food Choices, states that 35 percent of cancer deaths may be related to diet. The booklet states:
Diets rich in beta-carotene (the plant form of vitamin A) and vitamin C may reduce the risk of certain cancers.
Reducing fat in the diet may reduce cancer risk and, in helping weight control, may reduce the risk of heart attacks and strokes.
Diets high in fiber-rich foods may reduce the risk of cancers of the colon and rectum.
Vegetables from the cabbage family (cruciferous vegetables) may reduce the risk of colon cancer.FDA, in fact, authorized several health claims on food labels relating low-fat diets high in some plant-derived foods with a possibly reduced risk of cancer.
While FDA acknowledges that high intakes of fruits and vegetables rich in beta-carotene or vitamin C have been associated with reduced cancer risk, it believes the data are not sufficiently convincing that either nutrient by itself is responsible for the association. Nevertheless, since most fruits and vegetables are low-fat foods and may contain vitamin A (as beta-carotene) and vitamin C, the agency authorized a health claim relating diets low in fat and rich in these foods to a possibly reduced risk of some cancers.Another claim relates low-fat diets high in fiber-containing vegetables, fruits and grains to a possible reduction in cancer risk. (The National Cancer Institute recommends 20 to 30 grams of fiber a day.) Although the exact role of total dietary fiber, fiber components, and other nutrients and substances in these foods is not fully understood, many studies have shown such diets to be associated with reduced risk of some cancers.
Nutrition and Your Health:
Dietary Guidelines for Americans
Development of the 2005 Dietary Guidelines for Americans (sixth edition) Nutrition and Your Health: Dietary Guidelines for Americans is published jointly every 5 years by the Department of Health and Human Services (HHS) and the Department of Agriculture (USDA). The Guidelines provide authoritative advice for people two years and older about how good dietary habits can promote health and reduce risk for major chronic diseases. They serve as the basis for Federal food and nutrition education programs.The Department of Health and Human Services (HHS) and the Department of Agriculture (USDA) have begun the process of developing the sixth edition of Nutrition and Your Health: Dietary Guidelines for Americans. The Dietary Guidelines Advisory Committee, a committee of prominent experts in nutrition and health, will undertake a review of the 2000 Dietary Guidelines in light of recent scientific and applied literature and determine if revision is warranted. If so, the Committee will submit a report of its recommendations to assist the Departments in preparing the 2005 edition of the Dietary Guidelines.
Q: Why is fiber important to your diet? What can fiber do for you?
A: Numerous epidemiologic (population-based) studies have found that diets low in saturated fat and cholesterol and high in fiber are associated with a reduced risk of certain cancers, diabetes, digestive disorders, and heart disease. However, since high-fiber foods may also contain antioxidant vitamins, phytochemicals, and other substances that may offer protection against these diseases, researchers can't say for certain that fiber alone is responsible for the reduced health risks they observe, notes Joyce Saltsman, a nutritionist with FDA's Office of Food Labeling. "Moreover, no one knows whether one specific type of fiber is more beneficial than another since fiber-rich foods tend to contain various types," she adds. Recent findings on the health effects of fiber show it may play a role in:
Cancer: Epidemiologic studies have consistently noted an association between low total fat and high fiber intakes and reduced incidence of colon cancer. A 1992 study by researchers at Harvard Medical School found that men who consumed 12 grams of fiber a day were twice as likely to develop precancerous colon changes as men whose daily fiber intake was about 30 grams. The exact mechanism for reducing the risk is not known, but scientists theorize that insoluble fiber adds bulk to stool, which in turn dilutes carcinogens and speeds their transit through the lower intestines and out of the body.The evidence that a high-fiber diet can protect against breast cancer is equivocal. Researchers analyzing data from the Nurses' Health Study, which tracked 89,494 women for eight years, concluded in 1992 that fiber intake has no influence on breast cancer risk in middle-aged women. Previously, a review and analysis of 12 studies found a link between high fiber intake and reduced risk.In the early stages, some breast tumors are stimulated by excess amounts of estrogen circulating in the bloodstream. Some scientists believe that fiber may hamper the growth of such tumors by binding with estrogen in the intestine. This prevents the excess estrogen from being reabsorbed into the bloodstream.
Digestive disorders: Because insoluble fiber aids digestion and adds bulk to stool, it hastens passage of fecal material through the gut, thus helping to prevent or alleviate constipation. Fiber also may help reduce the risk of diverticulosis, a condition in which small pouches form in the colon wall (usually from the pressure of straining during bowel movements). People who already have diverticulosis often find that increased fiber consumption can alleviate symptoms, which include constipation and/or diarrhea, abdominal pain, flatulence, and mucus or blood in the stool.
Diabetes: As with cholesterol, soluble fiber traps carbohydrates to slow their digestion and absorption. In theory, this may help prevent wide swings in blood sugar level throughout the day. Additionally, a new study from the Harvard School of Public Health, published in the Feb. 12 issue of the Journal of the American Medical Association, suggests that a high-sugar, low-fiber diet more than doubles women's risk of Type II (non-insulin-dependent) diabetes. In the study, cereal fiber was associated with a 28 percent decreased risk, with fiber from fruits and vegetables having no effect. In comparison, cola beverages, white bread, white rice, and french fries increased the risk.
Heart Disease: Clinical studies show that a heart-healthy diet (low in saturated fat and cholesterol, and high in fruits, vegetables and grain products that contain soluble fiber) can lower blood cholesterol. In these studies, cholesterol levels dropped between 0.5 percent and 2 percent for every gram of soluble fiber eaten per day.As it passes through the gastrointestinal tract, soluble fiber binds to dietary cholesterol, helping the body to eliminate it. This reduces blood cholesterol levels, which, in turn, reduces cholesterol deposits on arterial walls that eventually choke off the vessel. There also is some evidence that soluble fiber can slow the liver's manufacture of cholesterol, as well as alter low-density lipoprotein (LDL) particles to make them larger and less dense. Researchers believe that small, dense LDL particles pose a bigger health threat.Recent findings from two long-term large-scale studies of men suggest that high fiber intake can significantly lower the risk of heart attack. Men who ate the most fiber-rich foods (35 grams a day, on average) suffered one-third fewer heart attacks than those who had the lowest fiber intake (15 grams a day), according to a Finnish study of 21,903 male smokers aged 50 to 69, published in the December 1996 issue of Circulation. Earlier in the year, findings from an ongoing U.S. study of 43,757 male health professionals (some of whom were sedentary, overweight or smokers) suggest that those who ate more than 25 grams of fiber per day had a 36 percent lower risk of developing heart disease than those who consumed less than 15 grams daily. In the Finnish study, each 10 grams of fiber added to the diet decreased the risk of dying from heart disease by 17 percent; in the U.S. study, risk was decreased by 29 percent.These results indicate that high-fiber diets may help blunt the effects of smoking and other risk factors for heart disease.
Obesity: Because insoluble fiber is indigestible and passes through the body virtually intact, it provides few calories. And since the digestive tract can handle only so much bulk at a time, fiber-rich foods are more filling than other foods--so people tend to eat less. Insoluble fiber also may hamper the absorption of calorie-dense dietary fat. So, reaching for an apple instead of a bag of chips is a smart choice for someone trying to lose weight. But be leery of using fiber supplements for weight loss. In August 1991, FDA banned methylcellulose, along with 110 other ingredients, in over-the-counter diet aids because there was no evidence these ingredients were safe and effective. The agency also recalled one product that contained guar gum after receiving reports of gastric or esophageal obstructions. The manufacturer had claimed the product promoted a feeling of fullness when it expanded in the stomach.
Q: What are tips for getting more fiber in your diet?
A: To fit more fiber into your day:
Read food labels. The labels of almost all foods will tell you the amount of dietary fiber in each serving, as well as the Percent Daily Value (DV) based on a 2,000-calorie diet. For instance, if a half cup serving of a food provides 10 grams of dietary fiber, one serving provides 40 percent of the recommended DV. The food label can state that a product is "a good source" of fiber if it contributes 10 percent of the DV--2.5 grams of fiber per serving. The package can claim "high in," "rich in" or "excellent source of" fiber if the product provides 20 percent of the DV--5 grams per serving.
Use the U.S. Department of Agriculture's food pyramid as a guide. If you eat 2 to 4 servings of fruit, 3 to 5 servings of vegetables, and 6 to 11 servings of cereal and grain foods, as recommended by the pyramid, you should have no trouble getting 25 to 30 grams of fiber a day.
Start the day with a whole-grain cereal that contains at least 5 grams of fiber per serving. Top with wheat germ, raisins, bananas, or berries, all of which are good sources of fiber.
When appropriate, eat vegetables raw. Cooking vegetables may reduce fiber content by breaking down some fiber into its carbohydrate components. When you do cook vegetables, microwave or steam only until they are al dente--tender, but still firm to the bite.
Avoid peeling fruits and vegetables; eating the skin and membranes ensures that you get every bit of fiber. But rinse with warm water to remove surface dirt and bacteria before eating. Also, keep in mind that whole fruits and vegetables contain more fiber than juice, which lacks the skin and membranes.
Eat liberal amounts of foods that contain unprocessed grains in your diet: whole-wheat products such as bulgur, couscous or kasha and whole-grain breads, cereals and pasta.
Add beans to soups, stews and salads; a couple of times a week, substitute legume-based dishes (such as lentil soup, bean burritos, or rice and beans) for those made with meat.
Keep fresh and dried fruit on hand for snacks.